1. Field of the Invention
The invention relates to a power transmission system for a hybrid vehicle, and particularly to an improvement of a hydraulic circuit that supplies oil for controlling, lubricating, and cooling a clutch, a motor, a transmission, and so on.
2. Description of Related Art
A power transmission system for a hybrid vehicle has been proposed, which includes a motor connected to a driving wheel through a transmission, and an engine connected to the motor through a clutch. A system described in Japanese Patent Application Publication No. 2012-111366 A (JP 2012-111366 A) is one example of such a power transmission system for a hybrid vehicle. The system generates hydraulic pressure by using a first oil pump connected to a pump impeller of a torque converter, and supplies oil for controlling, lubricating, and cooling to the transmission, the motor, and the clutch. The system also includes a second oil pump that suctions oil from an oil pan provided below the motor, and, forwards the oil to the first oil pump side. Japanese Patent Application Publication No. 2006-137406 A (JP 2006-137406 A) describes a technology for disengaging a clutch by using hydraulic pressure from an electric oil pump provided separately from the first oil pump.